E. F. Frolich and C. F. Ryan *

Reprint from CMS 1959

Several workers have recommended retaining foliage on the rootstock when grafting on one or two year old seedlings of Macadamia (1), (2), (3) Variable results have been observed when older rootstocks are defoliated at the time of grafting in California.

Investigations conducted at the University of California at Los Angeles some years ago showed a low percentage of grafts growing on one and two year old seedlings when all foliage was removed from the rootstock at the time of grafting. In the same experiments, grafts on rootstocks with foliage retained gave good percentages.

The availability of a block of four-year-old Macadamia seedlings for grafting at UCLA in late winter of 1957 made possible a study of the effect of retaining leaves on the rootstock with older materials. About 85% of the seedlings used in this experiment were Macadamia tetraphylla, the remainder were M. ternifolia. The scionwood was selected from one tree of the variety Kohala (HAES No. 386). All branches from which the scions were cut had been girdled by removing a ring of bark four months previous to the time of grafting. The rootstock seedlings were selected so as to have seedlings of about the same average size in each of three treatments. One treatment, rootstock defoliated, had all stock foliage removed at the time of grafting. A second treatment had about three fourths of the rootstock foliage removed at the time of grafting. In the third treatment only enough foliage was removed from the rootstock to facilitate placing the graft. Most of the scions were put on, as splice grafts but in some of the larger stumps a cleft graft was used (3).

Table I shows the percentage of scions growing nine months after grafting.

Table 1. Graft take of Macadamia ternifolia HAES No. 386 (Kohala)

*E F. Frolich in Laboratory Technician, and C. F. Ryan is instructor in the Department of Subtropical Horticulture, University of California at Los Angeles.

Fig. 1—Rootstock before grafting. Fig. 2—Rootstock not defoliated. Fig. 3—Rootstock three-fourths defoliated. Fig. 4—Rootstock defoliated.

No pruning was done on the scions. All scion buds that started were allowed to grow until termination of the experiment. New shoots from the rootstocks were removed at frequent intervals. On the rootstocks where the foliage was retained the number of stock leaves was gradually reduced by cutting off the terminal whorls from the remaining branches when the new shoots starting at the tips had become too numerous to remove economically. At the end of the experiment, however, there were still some mature leaves left on the rootstocks in the treatments where leaves were retained at the time of grafting.

Eleven months after grafting, all new shoot growth from the scions in each group was cut off and weighed. The results are shown in Table 2.

Table 2. Growth of Macadamia ternifolia HAES No. 386 (Kohala)

Grafted 3-22-57. Weighed 2-26-58

A few of the scions in the treatment where the rootstocks were completely defoliated made quite satisfactory growth, but the majorities were very poor. It would be impossible to predict for a given plant of the size used in the present experiment that it would be necessary to leave foliage on the stock. Taking the average of the three groups as a whole, however, there is a distinct advantage in keeping as much mature foliage on the rootstocks as is economically practical.

LITERATURE CITED